This invention relates to a variable capacity wobble plate compressor for compressing refrigerant circulated in an air conditioner for automotive vehicles, etc.
A conventional variable capacity wobble plate compressor of this kind has been proposed e.g. by Japanese Provisional Utility Model Registration Application (Kokai) No. 2-141682, which comprises a cylinder block having a plurality of cylinders formed therein and a bearing-receiving hole formed therethrough, a discharging space defined on one side of the cylinder block, a crankcase defined on the other side of same, a drive shaft having one end thereof supported by a bearing received in the bearing-receiving hole of the cylinder block, a wobble plate accommodated within the crankcase and fitted on the drive shaft, discharge valve means having a plurality of discharge valve elements for opening and closing respective outlet ports which communicate the cylinders with the discharging space, a fixing bolt fixing the discharge valve means to an end face of the cylinder block on the one side thereof, and capacity control means for changing pressure within the crankcase to thereby control the capacity or delivery quantity of the compressor, wherein the fixing bolt is formed therethrough with a high pressure-introducing passage for introducing high-pressure refrigerant gas within the discharging space into the bearing-receiving hole, whereby the high-pressure refrigerant gas introduced into the bearing-receiving hole is allowed to flow into the crankcase.
In the proposed variable capacity wobble plate compressor, the high pressure-introducing passage is provided for the purpose of introducing high pressure from the discharging chamber into the crankcase to thereby assist building-up of the pressure within the crankcase by blow-by gas (high-pressure refrigerant gas leaking through clearances between the cylinders and pistons sliding within the cylinders).
As shown in FIG. 1, the fixing bolt 300 used in the above compressor is formed therethrough with a high pressure-introducing passage consisting of a hexagon socket 301 formed in a head thereof, a medium diameter bore 302 continuous to the hexagon socket 301 and having a bore diameter A (e.g. A=3 mm), a restriction bore 303 having a bore diameter B (e.g. B=0.4 mm), and another medium diameter bore 304 having the same bore diameter as the first-mentioned medium diameter bore 302.
In general, in the conventional variable capacity wobble plate compressor described above, it is desirable to sufficiently cool and lubricate bearings used therein, especially a radial bearing and a thrust bearing in the bearing-receiving hole of the cylinder block.
According to the above compressor, in which the restriction bore 303 is provided in an intermediate portion of the high pressure-introducing passage formed though the fixing bolt 300, the high-pressure refrigerant gas introduced from the discharging chamber undergoes adiabatic expansion to fall in temperature upon entering the medium diameter bore 304 through the restriction bore 303. However, the ratio of expansion of the gas is only 7.5 (i.e. A (3 mm)/B (0.4 mm)), and accordingly the temperature falling amount is not so large. As a result, the high-pressure refrigerant gas from the discharging space is introduced to the bearings within the cylinder block without being much lowered in temperature while passing through the high pressure-introducing passage. Therefore, the bearings cannot be sufficiently cooled by the high-pressure refrigerant gas from the discharging space.
Further, in the conventional variable capacity wobble plate compressor, the restriction bore 303 is provided at an intermediate portion of the high pressure-introducing passage formed through the fixing bolt 300. Therefore, in machining the high pressure-introducing passage through the fixing bolt 300, it is required to effect boring of the fixing bolt two times, i.e. form the medium diameter bore 302 on one side of a wall through which the restriction bore 303 is formed and form the medium diameter bore 304 on the other side of the wall. This increases the number of machining steps of the fixing bolt, which results in an increased manufacturing cost.